• Bulletin of the Korean Chemical Society
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• 제34권3호
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• pp.801-809
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• 2013

We investigate sensitivity and limit of detection (LOD) of trace copper (Cu) metal using pristine carbon nanotube (CNT) and acidified CNT (ACNT) electrodes. Squarewave based anodic stripping voltammetry (SWASV) is used to determine the stripped Cu concentration. Prior to performing the SWASV measurements, its optimal conditions are determined and with that, effects of potential scan rate and $Cu^{2+}$ concentration on stripping current are evaluated. The measurements indicate that (1) ACNT electrode shows better results than CNT electrode and (2) stripping is controlled by surface reaction. In the given $Cu^{2+}$ concentration range of 25-150 ppb, peak stripping current has linearity with $Cu^{2+}$ concentration. Quantitatively, sensitivity and LOD of Cu in ACNT electrode are 9.36 ${\mu}A\;{\mu}M^{-1}$ and 3 ppb, while their values are 3.99 ${\mu}A\;{\mu}M^{-1}$ and 3 ppb with CNT electrode. We evaluate the effect of three different water solutions (deionized water, tap water and river water) on stripping current and the confirm types of water don't affect the sensitivity of Cu. It turns out by optical inspection and cyclic voltammetry that superiority of ACNT electrode to CNT electrode is attributed to exfoliation of CNT bundles and improved interfacial adhesion occurring during oxidation of CNTs.

• E2M - 전기 전자와 첨단 소재
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• 제9권6호
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• pp.572-577
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• 1996

Alternating current and direct current of pure, ball milled, and $Al_{2}$O$_{3}$ added ZnO were investigated by means of complex impedance measurement and voltage-current source measurement unit. The electrical conductivity of A1$_{2}$O$_{3}$ added ZnO samples increases when the content of A1$_{2}$O$_{3}$ is used within 1 at% and decreases when it's used more than that. The increase and decrease of electrical conductivity seem to be the donor effect of $Al_{2}$O$_{3}$ and the increase of the number of ZnO grains, respectively. Impedance spectrum seems to be one semircicle. The size of semicircle increase with increasing the A1$_{2}$O$_{3}$ contents. The calculated dielectric constant(at 50.deg. C) were about 70-140 at the peak of the semicircle. The semicircles seem not to be the resistance of ZnO grain as compared to that of 10 for pure ZnO.

• 항공우주산업기술동향
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• 제8권1호
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• pp.3-11
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• 2010

세계적인 불경기에도 불구하고 세계 우주시장은 전년대비 11% 증가하여 2009년 최대치인 1,609억불에 도달하였다. 세계 각국의 우주 분야 투자도 전년대비 10% 증가한 680억불에 이르렀다. 반면 우리나라의 우주분야 예산은 2009년 2억 1,700억불로 전년대비 24% 감소하였다. 나로호 개발이 완료됨에 따라 개발 주기에 따른 예산 감소의 영향으로 분석된다. 우주시장 역시 불경기에 따른 위성 핸드폰 등의 수출 감소로 전년 대비 3% 감소한 8,644억 원으로 조사되었다. 본 논문에서는 세계 각국 및 우리나라의 우주분야 투자와 우주시장 현황을 정리하였고, 우리나라 예산정책에 관한 시사점을 제고해보았다.

• 대한전자공학회논문지SD
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• 제37권11호
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• pp.96-104
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• 2000

본 논문은 정적 CMOS 회로의 단락전류로 인한 전력 소모을 구하기 위한 간단한 방법을 제시한다. 단락전류식은 게이트와 드레인 사이에 존재하는 커플링 커패시턴스의 영향을 고려하여 실제 전류 파형의 극점을 정확하게 보간함으로써 유도하였다. 트랜지스터의 출력 파형을 조사한 후 모형화한 전류 수식을 기반으로 CMOS 회로의 지연 시간을 예측하기 위한 거시모형과 수식들을 제안하였다. 제안된 방법은 시뮬레이션을 통하여 현재의 기술 동향 특성인 신호 천이시간과 부하 커패시턴스가 감소하는 경우에 대해 이전의 연구보다 더욱 정확하고 신속히 예측할 수 있음을 보였다. 또한 제안된 거시모형은 전류식이 변할지라도 전력 소모를 계산하는데 쉽게 적용이 가능하다.

• 대한기계학회논문집A
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• 제29권8호
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• pp.1118-1122
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• 2005

The direct current potential drop (DCPD) method and the unloading compliance (UC) method with a crack opening displacement gauge were applied simultaneously to the Zr-2.5Nb curved compact tension (CCT) specimens to determine which of the two methods can precisely determine the crack initiation point and hence the crack length for evaluation of their fracture toughness. The DCPD method detected the crack initiation at a smaller load-line displacement compared to the UC method. As a verification, a direct observation of the fracture surfaces on the curved compact tension specimens was made on the CCT specimens experiencing either 0.8 to 1.0 mm load line displacement or various loads from $50\%\;to\;80\%$ of the maximum peak load, or $P_{max}$. The DCPD method is concluded to be more precise in determining the crack initiation and fracture toughness, J in Zr-2.5Nb CCT specimens than the UC method.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2006년도 전력전자학술대회 논문집
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• pp.488-491
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• 2006

In this paper proposed method of maximum power point tracking using boost converter for a connected single phase inverter with photovoltaic system. The maximum power point tracking control is based on generated circuit control MOSFET switch of boost converter and single phase inverter uses predicted current control to control four IGBT's switch in full bridge. The predicted current control provide current with sinusoidal wave shape and inphase with voltage. The generation control circuit allows each photovoltaic module to operate independently at peak capacity, simply by detecting of the output power of the system. Furthermore, the generation control circuit attenuates low-frequency ripple voltage, which is caused by the full-bridge inverter, across the photovoltaic modules. Consequently, the output power of system is increased due to the increase in average power generated by the photovoltaic modules. The effectiveness of the proposed inverter system is confirmed experimentally and by means of simulation.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
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• pp.84-87
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• 2003

HgTe quantum dots(QDs) were synthesized in aqueous solution by colloidal method. The absorption and photoluminescence(PL) spectrum of the synthesized HgTe QDs revealed the strong exitonic peak in the IR region. And the photocurrent measurement of colloidal QDs are performed using IR light source. The lineshape of the wavelength dependent intensity of photocurrent was very similar to the absorption spectrum, indicating the charges generated by the absorption of photons give direct contribution to photocurrent. The channels of dark current are supposed $H_2O$ containing in thiol by the remarkable drop of current at the state of vacuum. It was thought that the proper passivation layer on the top of HgTe film reduce the dark current and the adequate choice of capping material improves the efficiency of the photocurrent in the HgTe QDs. This study suggests that HgTe QDs are very prospective materials for optoelectronics including photodetectors in the IR range.

• Journal of Power Electronics
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• 제11권4호
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• pp.499-506
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• 2011

This paper presents an interleaved active-clamping zero-voltage-switching (ZVS) forward-flyback converter without an output choke. The presented topology has two active-clamping circuits with two separated transformers. Because of the interleaved operation of the converter, the output current ripple will be reduced. The proposed converter can approximately share the total load current between the two secondaries. Therefore, the transformer copper loss and the rectifier diodes conduction loss can be decreased. The output capacitor is made of two series capacitors which reduces the peak reverse voltage of the rectifier diodes. The circuit has no output inductor and few semiconductor elements, such that the adopted circuit has a simpler structure, a lower cost and is suitable for high power density applications. A detailed analysis and the design of this new converter are described. A prototype converter has been implemented and experimental results have been recorded with an ac input voltage of 85-135Vrms, an output voltage of 12V and an output current of 16A.

• The Journal of Korean Physical Therapy
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• 제21권4호
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• pp.73-79
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• 2009

Purpose: Recently, neurostimulation studies involving manipulation of cortical excitability of the human brain have been increasingly attempted. We investigated whether transcranial direct current stimulation (tDCS) applied to the underlying cerebral cortex, directly induces cortical activation during fMRI scanning. Methods: We recently recruited five healthy subjects without a neurological or psychiatric history and who were right-handed, as verified by the modified Edinburg Handedness Inventory. fMRI was done while constant anodal tDCS was delivered to the underlying SM1 area?? immediately after the pre-stimulation for eighteen minutes. Results: Group analysis yielded an averaged map that showed that the SM1 area and the superior parietal cortex in the ipsilateral hemisphere were activated. The voxel size and peak intensity were, respectively, 82 and 5.22 in the SM1, and 85 and 5.77 in the superior parietal cortex. Conclusion: Cortical activation can be induced by constant anodal tDCS of the underlying motor cortex. This suggests that tDCS may be an effective therapeutic device for enhancing? physical motor function by modulating neural excitability of the motor cortex.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 E
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• pp.1800-1802
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• 1998

The Pohang Light Source (PLS) is a third generation 2 GeV synchrotron machine. An injection kicker modulator is positioned in the PLS storage ring tunnel. The kicker modulator is driving four kicker magnets simultaneously. The kicker magnets produce magnetic field to deflect the stored beam orbit in the storage ring closer to the injected beam from the PLS beam transfer line. The injected beam then falls into the storage ring beam dynamic aperture. The current kicker modulator was upgraded and installed on August 1995. Since then, the kicker modulator has shown very reliable and stable performance. The kicker modulator specifications are ${\sim}6.0{\mu}s$ full width, ${\sim}24$ kA peak current, and 10 Hz repetition rate. Output current waveform is a half sinusoid. Two thyratron switches(EEV CX-1536AX) are used in the kicker modulator. Total accumulated thyratron heater run hour is about 15,000 hours as of May 1998. Measurement result of spatial magnetic field distribution in the kicker magnet shows good uniformity.